Electron beam induced deposition of interface to carbon nanotube

ABSTRACT

A system and method are provided for fabricating a low electric resistance ohmic contact, or interface, between a Carbon Nanotube (CNT) and a desired node on a substrate. In one embodiment, the CNT is a Multiwalled, or Multiwall, Carbon Nanotube (MWCNT), and the interface provides a low electric resistance ohmic contact between all conduction shells, or at least a majority of conduction shells, of the MWCNT and the desired node on the substrate. In one embodiment, a Focused Electron Beam Chemical Vapor Deposition (FEB-CVD) process is used to deposit an interface material near an exposed end of the MWCNT in such a manner that surface diffusion of precursor molecules used in the FEB-CVD process induces lateral spread of the deposited interface material into the exposed end of the MWCNT, thereby providing a contact to all conduction shells, or at least a majority of the conduction shells, of the MWCNT.

FIELD OF THE DISCLOSURE

This disclosure relates to fabrication of an interface between a CarbonNanotube (CNT) and a desired node on a substrate.

BACKGROUND

Low-resistance, stable contacts are critical for the performance andreliability of integrated circuits. As such, the preparation andcharacterization of contacts for integrated circuits demand majorefforts in circuit fabrication. Conventional techniques for fabricatingcontacts are fundamentally flawed in making low resistance contactsbetween Multiwalled Carbon Nanotubes (MWCNTs) or MWCNT-based devices andmetal pads or wires. Specifically, conventional techniques lack thelevel of control on nanoscale required for making a precise connectionto MWCNTs and, most importantly, can only be used to establish electriccontact to the outer conduction shell of the MWCNT. As such, a majorityof the conduction channels through the inner shells of the MWCNT cannotbe utilized, thus negating a key advantage of MWCNTs as highly efficientmulti-channel electric conductors.

SUMMARY

The present disclosure describes a system and method for fabricating alow electric resistance ohmic contact, or interface, between a CarbonNanotube (CNT) and a desired node on a substrate. In one embodiment, theCNT is a Multiwalled, or Multiwall, Carbon Nanotube (MWCNT), and theinterface provides a low electric resistance ohmic contact between allconduction shells, or at least a majority of conduction shells, of theMWCNT and the desired node on the substrate. In one embodiment, aFocused Electron Beam Chemical Vapor Deposition (FEB-CVD) process, whichis also referred to as Electron Beam Induced Deposition (EBID) process,is used to deposit an interface material near an exposed end of theMWCNT in such a manner that surface diffusion of precursor moleculesused in the FEB-CVD process induces lateral spread of the depositedinterface material into the exposed end of the MWCNT. As a result of thelateral spread of the deposited interface material into the exposed endof the MWCNT, the interface material provides a contact to allconduction shells, or at least a majority of the conduction shells, ofthe MWCNT. The deposited interface material provides a low electricresistance ohmic contact between the MWCNT and the desired node on thesubstrate.

More specifically, in one embodiment, a MWCNT is first aligned betweentwo electrically conducting interconnects on a substrate. Each of theelectrically conducting interconnects may be, for example, a metallicinterconnect, an electrically conducting polymer interconnect, agraphene interconnect, or the like. The substrate may be, for example, asemiconductor substrate, a dielectric substrate, or the like. If theends of the MWCNT do not expose inner shells of the MWCNT, the ends ofthe MWCNT are cut to expose the inner shells of the MWCNT using atechnique such as, for example, Focused Ion Beam (FIB) milling. Next,for each of the exposed ends of the MWCNT, a FEB-CVD process isperformed wherein a primary electron beam is focused near the exposedend of the MWCNT. As a result, an interface material is deposited nearthe exposed end of the MWCNT such that, during deposition, the interfacematerial laterally spreads into the exposed end of the MWCNT and makescontact to all of the conduction shells, or at least a majority of theconduction shells, of the MWCNT. Further, in one embodiment, a timing ofan on/off regime of the primary electron beam is controlled such thatsurface diffusion of precursor molecules used in the FEB-CVD process hassufficient time to induce lateral spread of the deposited interfacematerial into the exposed end of the MWCNT. A shape and size of thedeposited interface material may be controlled via parameters of theFEB-CVD process. The shape of the deposited interface as well as thesize of the contact area of the interface material to both the MWCNT andthe electrically conducting interconnect define the interface thermalresistance between the MWCNT and the electrically conductinginterconnect.

In another embodiment, one end of the MWCNT is aligned with an end of asecond MWCNT. If the aligned ends of the MWCNTs do not expose innershells of the MWCNTs, the aligned ends of the MWCNTs are cut to exposethe inner shells of the MWCNTs using a technique such as, for example,FIB milling. Next, a FEB-CVD process is performed wherein a primaryelectron beam is focused near the aligned exposed ends of the MWCNTs. Asa result, an interface material is deposited near the aligned exposedends of the MWCNTs such that, during deposition, the interface materiallaterally spreads into the aligned exposed ends of the MWCNTs and makescontact to all of the conduction shells, or at least a majority of theconduction shells, of the MWCNTs. Further, in one embodiment, a timingof an ON/OFF regime of the primary electron beam is controlled such thatsurface diffusion of precursor molecules used in the FEB-CVD process hassufficient time to induce lateral spread of the deposited interfacematerial into the aligned exposed ends of the MWCNTs. A shape and sizeof the deposited interface material may be controlled via parameters ofthe FEB-CVD process. The shape of the deposited interface as well as thesize of the contact area of the interface material to the MWCNTs definethe interface thermal resistance between the MWCNTs.

In one embodiment, the deposited interface material is amorphous carbon(a-C), and post-processing is used to lower an electric resistance ofthe deposited interface material while maintaining contact between themetal pad/wire and the MWCNT. More specifically, an annealing processinduced by either direct heating (thermal) or by passing an electriccurrent through the interface (electric) may be performed to providetotal or partial graphitization of the deposited carbon interfacematerial, thereby substantially reducing the electric resistance of thedeposited carbon interface material. In another embodiment, thedeposited interface material is a metallic material and the precursormolecule is an organometallic compound.

Those skilled in the art will appreciate the scope of the presentinvention and realize additional aspects thereof after reading thefollowing detailed description in association with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thisspecification illustrate several aspects of the invention, and togetherwith the description serve to explain the principles of the invention.

FIGS. 1A-1C graphically illustrate fabrication of interfaces between aMultiwalled Carbon Nanotube (MWCNT) and electrically conductinginterconnects on a substrate according to one embodiment of the presentdisclosure;

FIG. 2 graphically illustrates a Focused Electron Beam Chemical VaporDeposition (FEB-CVD) process, which is also referred to as an ElectronBeam Induced Deposition (EBID) process, that is preferably utilized tofabricate the interfaces for a MWCNT of FIG. 1 according to oneembodiment of the present disclosure;

FIG. 3 is a flow chart illustrating a process for fabricating aninterface for a MWCNT according to one embodiment of the presentdisclosure;

FIGS. 4A through 4C graphically illustrate fabrication of an interfacebetween MWCNTs according to another embodiment of the presentdisclosure; and

FIG. 5 illustrates a FEB-CVD system for fabricating an interface for aMWCNT on a substrate according to one embodiment of the presentdisclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the invention and illustratethe best mode of practicing the invention. Upon reading the followingdescription in light of the accompanying drawings, those skilled in theart will understand the concepts of the invention and will recognizeapplications of these concepts not particularly addressed herein. Itshould be understood that these concepts and applications fall withinthe scope of the disclosure and the accompanying claims.

FIGS. 1A through 1C graphically illustrate a process for fabricatinginterfaces 10 and 12 between a Carbon Nanotube (CNT) 14 and electricallyconducting interconnects 16 and 18 (hereinafter interconnects 16 and 18)on a substrate 20 according to one embodiment of this disclosure.Preferably, the CNT 14 is a Multiwalled, or Multiwall, Carbon Nanotube(MWCNT) 14 and will be referred to as such for much of this disclosure.However, in an alternative embodiment, the CNT 14 is a Single WalledCNT. As will be appreciated by one of ordinary skill in the art, theMWCNT 14 includes multiple conduction shells, or conduction layers, ofcarbon, which is typically in the form of graphite. The multipleconduction shells may be in a spiral pattern such that a cross-sectionof the MWCNT 14 is a spiral pattern. Alternatively, the multipleconduction shells in the MWCNT 14 may be concentric tubes such that across-section of the MWCNT 14 is a set of concentric circles. Each ofthe interconnects 16 and 18 is formed of an electrically conductingmaterial and may be, for example, a metallic interconnect (e.g., a metalpad or wire), an electrically conducting polymer interconnect, agraphene interconnect, or the like. The substrate 20 may be any type ofsuitable substrate such as, for example, a semiconductor substrate, adielectric substrate, or the like.

In this embodiment, a Focused Electron Beam Chemical Vapor Deposition(FEB-CVD) process, which may also be referred to as an Electron BeamInduced Deposition (EBID) process, is used to form the interfaces 10 and12 between the MWCNT 14 and the interconnects 16 and 18 on the substrate20. By taking advantage of surface diffusion of precursor molecules andcontrolling a location of a primary, or high energy, electron beam(e-beam) used in the FEB-CVD process, the interfaces 10 and 12 arefabricated with nanometer resolution such that there are low electricresistance ohmic contacts formed between all conduction shells, or atleast a majority of the conduction shells, of the MWCNT 14 and theinterconnects 16 and 18 on the substrate 20.

Before continuing with the discussion of FIGS. 1A through 1C, adiscussion of FED-CVD is beneficial. FIG. 2 graphically illustrates anexemplary FEB-CVD process. In this FEB-CVD process, a tightly-focused,high-energy primary e-beam impinges on a substrate. High energy primaryelectrons from the primary e-beam interact with the substrate to producelow energy secondary electrons. A precursor gas is introduced into areaction chamber either via flooding from a smaller reaction cell withinthe reaction chamber with the precursor gas, local injection of theprecursor gas using very a fine needle, or as a residual speciespre-adsorbed on the substrate which is commonly referred to as asubstrate contamination.

Once adsorbed on the substrate surface, precursor molecules from theprecursor gas continuously redistribute on the substrate by surfacediffusion. Interactions of adsorbed precursor molecules withback-scattered primary and secondary electrons of the appropriate energyresult in dissociation of the precursor molecules and formation of adeposit. As will be appreciated by one of ordinary skill in the art, theprecursor gas is selected such that the deposit is formed of a desiredmaterial. For example, methane may be selected as the precursor gas inan embodiment where the deposit is desired to be carbon. Note that avariety of materials such as carbon, metals, and like may be depositedvia FEB-CVD by selection of the appropriate precursor gas, as will beappreciated by one of ordinary skill in the art upon reading thisdisclosure. Note that the FEB-CVD process is a room temperature processand is therefore compatible with electronics fabrication processes suchas Complementary Metal Oxide Semiconductor (CMOS) fabrication processes.

Returning to FIGS. 1A through 1C, FIG. 1A illustrates the fabrication ofthe interfaces 10 and 12 at an initial point in time (t_(initial))during the fabrication process. As illustrated, the MWCNT 14 is alignedbetween the interconnects 16 and 18. In this embodiment, theinterconnects 16 and 18 are, for example, contact pads or wires formedof an electrically conducting material. The interfaces 10 and 12 areformed at exposed ends 22 and 24, respectively, of the MWCNT 14. Theexposed ends 22 and 24 of the MWCNT 14 expose the inner conductionshells of the MWNCT 14. For the interface 10, the primary e-beam usedfor the FEB-CVD process is focused near the exposed end 22 of the MWCNT14. Preferably, the primary e-beam is focused approximately 0 nanometers(nm) (i.e., right at the edge of the exposed end 22 of the MWNT 14) to500 nm from the exposed end 22 of the MWCNT 14. Likewise, for theinterface 12, the primary e-beam used for the FEB-CVD process is focusednear the exposed end 24 of the MWCNT 14. Preferably, the primary e-beamis focused approximately 0 nm (i.e., right at the edge of the exposedend 24 of the MWNT 14) to 500 nm from the exposed end 24 of the MWCNT14. By focusing the primary e-beam near the exposed ends 22 and 24 ofthe MWCNT 14, an interface material is deposited near the exposed ends22 and 24 of the MWCNT 14 and, in this embodiment, over theinterconnects 16 and 18. In one embodiment, the interface material isa-C. In another embodiment, the interface material is a metal such as,for example, Copper, Platinum, Tungsten, or the like. Again, theinterface material can be selected by utilizing the appropriateprecursor compound.

FIG. 1B illustrates the interfaces 10 and 12 at an intermediate time(t_(intermediate)) in the fabrication process. As illustrated, surfacediffusion of the precursor molecules has induced lateral spread of thedeposited interface material into the MWCNT 14 at the exposed ends 22and 24 of the MWCNT 14. In one embodiment, timing of an ON/OFF regime,or sequence, for the primary e-beam is controlled such that surfacediffusion of the precursor molecules is given sufficient time to inducelateral spread of the deposited interface material into the exposed ends22 and 24 of the MWCNT 14. As will be appreciated by one of ordinaryskill in the art upon reading this disclosure, the amount of time thatis sufficient to induce lateral spread of the deposited interfacematerial into the exposed ends 22 and 24 may vary depending on variousparameters such as, but not limited to, a surface diffusion coefficientfor the precursor molecules on the surface of the substrate 20, thephysico-chemical nature of the precursor molecule and the substrate 20,the deposition conditions (pressure, temperature), among other factorsand a distance between the primary e-beam and the exposed ends 22 and 24of the MWCNT 14.

FIG. 1C illustrates the interfaces 10 and 12 at a final time (t_(final))in the fabrication process. At this point, deposition of the interfacematerial is complete. As illustrated, surface diffusion of the precursormolecules has continued to induce lateral spread of the depositedinterface material into the MWCNT 14 such that the deposited interfacematerial atomically fills and establishes an electric contact to allconduction shells (both inner and outer), or at least a majority of theconduction shells, of the MWCNT 14 at the exposed ends 22 and 24 of theMWCNT 14. Again, in one embodiment, timing of an ON/OFF regime, orsequence, for the primary e-beam is controlled such that surfacediffusion of the precursor molecules is given sufficient time to inducelateral spread of the deposited interface material into the exposed ends22 and 24 of the MWCNT 14.

In one embodiment, fabrication of the interfaces 10 and 12 is completedvia post processing. More specifically, the interfaces 10 and 12 may beannealed by either direct heating (thermal) or by passing an electriccurrent through the interface (electric). For example, in oneembodiment, the deposited interface material is a-C, which, due to itsamorphous structure, is an insulator rather than a conductor. Bythermally or electrically annealing the deposited interface material,the a-C is partially or totally graphitized. In other words, via thermalor electric annealing, the deposited carbon transitions from a-C, whichis insulating, to partially or totally graphitized carbon, which isconducting. As a result, after post processing, the interfaces 10 and 12are ohmic contacts having low electric resistivity. Note that in theembodiment where the deposited interface material is a-C, after postprocessing, the electric resistivity of the interfaces 10 and 12 is lowboth because of the conductivity of the partially or totally graphitizedcarbon interfaces 10 and 12 and because the partially or totallygraphitized carbon interfaces 10 and 12 have a crystalline structurethat is the same as, or similar to, that of the conduction shells of theMWCNT 14.

FIG. 3 is a flow chart illustrating a process for fabricating theinterfaces 10 and 12 between the MWCNT 14 and the interconnects 16 and18 on the substrate 20 according to one embodiment of this disclosure.First, the MWCNT 14 is aligned between the interconnects 16 and 18 (step100). The MWCNT 14 may be aligned between the interconnects 16 and 18using any suitable technique. In one embodiment, a droplet of MWCNTsolution is placed on a region of the substrate 20 containing theinterconnects 16 and 18. A Direct Current (DC), Alternating Current(AC), or DC-AC potential is then applied on one of the interconnects 16and 18, the other one of the interconnects 16 and 18 is allowed toremain floating, and a third interconnect (not shown) in the region isgrounded. A strength of the resulting non-uniform interelectrodeelectric field is controlled to overcome Brownian motion such that theMWCNT 14, which is within the MWCNT solution, aligns between theinterconnects 16 and 18. While not essential, for a more detaileddiscussion of an exemplary process for aligning the MWCNT 14 between theinterconnects 16 and 18, the interested reader is directed to J. W. Songet al., “Characterization and air pressure sensing of doubly clampedmulti-walled carbon nanotubes,” 19 Nanotechnology 4 (2008), which ishereby incorporated herein by reference for its teaching relating toaligning a MWCNT between electrodes.

Next, the ends of the MWCNT 14 are cut to expose the inner conductiveshells of the MWCNT 14, thereby providing the exposed ends 22 and 24 ofthe MWCNT 14 (step 102). Note that some MWCNTs may already have exposedends and therefore do not need to be cut. As such, step 102 may not beneeded for all types of MWCNTs. Any suitable process for cutting theends of the MWCNT 14, or otherwise opening the ends of the MWCNT 14 toexpose the inner conduction shells, may be used. In one embodiment,localized water assisted electron beam etching and Focused Ion Beam(FIB) cutting is used to cut the ends of the MWCNT 14 to expose theinner conduction shells. More specifically, if small amounts of watervapor are introduced into the microscope chamber, the MWCNT 14 may becut by focusing the primary e-beam at the desired location to perform anetching process. The carbon forming the MWCNT 14 may be etched as aresult of the reaction C+2H₂O→CO₂+2H₂ with ΔH=−82.4 kilojoules per mole(kJ/mol). Carbon can also be removed from the MWCNT 14 by exothermicreactions C+O₂→CO₂ and C+½H₂→CH with oxygen and hydrogen originatingeither from the environment or the water reaction.

A FEB-CVD process is then performed to deposit a desired interfacematerial near the exposed ends 22 and 24 of the MWCNT 14 such that,during deposition, the interface material laterally spreads into theMWCNT 14, thereby atomically filling and making contact to allconduction shells (both inner and outer), or at least a majority of theconduction shells, of the MWCNT 14 at the exposed ends 22 and 24 of theMWCNT 14 (step 104). As discussed above, the primary e-beam used for theFEB-CVD process is focused near the exposed end 22 of the MWCNT 14.During deposition of the desired interface material, surface diffusionof the precursor molecules induces lateral spread of the interfacematerial into the MWCNT 14 such that the interface 10 connects to allconduction shells, or at least most conduction shells, of the MWCNT 14.Likewise, the primary e-beam used for the FEB-CVD process is focusednear the exposed end 24 of the MWCNT 14. During deposition of thedesired interface material, surface diffusion of the precursor moleculesinduces lateral spread of the interface material into the MWCNT 14 suchthat the interface 12 connects to all conduction shells, or at leastmost conduction shells, of the MWCNT 14.

Note that various parameters of the FEB-CVD process may be adjusted tocontrol a size and shape of the interfaces 10 and 12 to an arbitrarydegree as well as to control the growth rate of the interfaces 10 and12. For instance, primary e-beam current, primary e-beam energy, primarye-beam diameter, deposition chamber pressure and temperature, depositiontime, precursor delivery scheme, or any combination thereof may becontrolled to grow the interfaces 10 and 12 in a desired shape and sizeat an acceptable growth rate. As an example, the interfaces 10 and 12may be grown using a Scanning Electron Microscope (SEM) as the source ofthe primary e-beam in a high vacuum of 10-6 Torr with no additionalprecursor gases introduced by keeping the primary e-beam focused for atime period between 2.5 minutes and 25 minutes with a e-beamaccelerating voltage or energy in the range of 15-30 kiloelectron volts(keV) and with a primary e-beam current in the range of approximately350-450 picoamps (pA). While not essential, for more informationregarding the effects of the FEB-CVD process parameters on the size andshape of the interfaces 10 and 12 and the growth rate of the interfaces10 and 12, the interested reader is directed to Andrei G. Fedorov etal., “Transport issues in focused electron beam chemical vapordeposition,” 201 Surface & Coatings Technology 8808 (2007), KonradRykaczewski et al., “Analysis of electron beam induced deposition (EBID)of residual hydrocarbons in electron microscopy,” 101 Journal of AppliedPhysics 054307 (2007), Konrad Rykaczewski et al. “Dynamic growth ofcarbon nanopillars and microrings in electron beam induced dissociationof residual hydrocarbons,” 108 Ultramicroscopy 989 (2008), and WilliamB. White et al., “What Controls Deposition Rate in Electron-BeamChemical Vapor Deposition?,” 97 Physical Review Letters 086101 (2006),each of which is incorporated herein by reference for their teachings onthe effect of FEB-CVD parameters on the size and shape of the depositand the growth rate of the deposit.

Once the interfaces 10 and 12 are deposited, post-processing may beperformed (step 106). Note that post-processing may not be needed forall types of interface materials. In one embodiment, the depositedinterface material is a-C. For a-C, thermal or electric annealing isused to provide total or partial graphitization of the a-C therebycausing the interfaces 10 and 12 to transition from insulating toconducting. At this point, the carbon interfaces 10 and 12 have alow-electric resistance as a result of the post-processing and the factthat the crystalline structure of the carbon interfaces 10 and 12 is thesame as, or similar to, that of the conduction shells of the MWCNT 14.Once post-processing is complete, the interfaces 10 and 12 provide lowelectric resistance ohmic contacts to all of the conduction shells, orat least a majority of the conduction shells, of the MWCNT 14.

FIGS. 4A through 4C graphically illustrate a process for fabricating aninterface 26 between CNTs 28 and 30 on a substrate 32 according toanother embodiment of the present disclosure. Preferably, the CNTs 28and 30 are MWCNTs 28 and 30 and, therefore, will be referred to as suchfor much of this disclosure. However, in an alternative embodiment, theCNTs 28 and 30 are Single Walled CNTs. Note that while FIGS. 4A through4C illustrate two MWCNTs 28 and 30, this process may be used to createan interface between more than two MWCNTs such that the interface 26connects aligned ends of the more than two MWCNTs. For example, one endof each of three MWCNTs may be aligned such that the interface 26connects the aligned ends of the three MWCNTs.

The process of FIGS. 4A through 4C is substantially the same as thatdescribed above. FIG. 4A illustrates the fabrication of the interface 26at an initial point in time (t_(initial)). As illustrated, an end 34 ofMWCNT 28 has been aligned with an end 36 of the MWCNT 30 using anysuitable technique. Depending on whether the ends 34 and 36 of theMWCNTs 28 and 30, respectively, are already exposed, the ends 34 and 36may be cut using, for example, an FIB cutting process to expose theinner shells of the MWCNTs 28 and 30, which are hereinafter referred toas exposed ends 34 and 36. A primary e-beam used for the FED-CVD processis focused near the exposed ends 34 and 36 of the MWCNTs 28 and 30.Preferably, the primary e-beam is focused in the range of and includingapproximately 0 nm (i.e., right at the edge of the exposed end of theMWNT) to 500 nm from each of the exposed ends 34 and 36 of the MWCNTs 28and 30. By focusing the primary e-beam near the exposed ends 34 and 36of the MWCNTs 28 and 30, an interface material is deposited near theexposed ends 34 and 36 of the MWCNTs 28 and 30. In one embodiment, theinterface material is a-C. In another embodiment, the interface materialis a metal such as, for example, Copper, Platinum, Tungsten, or theothers. Again, the interface material can be selected by utilizing theappropriate precursor compound.

FIG. 4B illustrates the interface 26 at an intermediate time(t_(intermediate)) in the fabrication process. As illustrated, surfacediffusion of the precursor molecules has induced lateral spread of thedeposited interface material into the exposed ends 34 and 36 of theMWCNTs 28 and 30. In one embodiment, timing of an ON/OFF regime, orsequence, for the primary e-beam is controlled such that surfacediffusion of the precursor molecules is given sufficient time to inducelateral spread of the deposited interface material into the exposed ends34 and 36 of the MWCNTs 28 and 30. As will be appreciated by one ofordinary skill in the art upon reading this disclosure, the amount oftime that is sufficient to induce lateral spread of the depositedinterface material into the exposed ends 34 and 36 of the MWCNTs 28 and30 may vary depending on various parameters such as, but not limited to,a surface diffusion coefficient for the precursor molecules on thesurface of the substrate 32, the physico-chemical nature of theprecursor molecule and the substrate 32, the deposition conditions(pressure, temperature), among other factors and a distance between theprimary e-beam and the exposed ends 34 and 36 of the MWCNTs and 30.

FIG. 4C illustrates the interface 26 at a final time (t_(final)) in thefabrication process. At this point, deposition of the interface materialis complete. As illustrated, surface diffusion of the precursormolecules has continued to induce lateral spread of the depositedinterface material into the exposed ends 34 and 36 of the MWCNTs 28 and30 such that the deposited interface material atomically fills andestablishes an electric contact to all conduction shells (both inner andouter), or at least a majority of the conduction shells, of the MWCNTs28 and 30 at the exposed ends 34 and 36 of the MWCNTs 28 and 30. Again,in one embodiment, timing of an ON/OFF regime, or sequence, for theprimary e-beam is controlled such that surface diffusion of theprecursor molecules is given sufficient time to induce lateral spread ofthe deposited interface material into the exposed ends 34 and 36 of theMWCNTs 28 and 30.

In one embodiment, fabrication of the interface 26 is completed via postprocessing. More specifically, the interface 26 may be annealed byeither direct heating (thermal) or by passing an electric currentthrough the interface (electric). For example, in one embodiment, thedeposited interface material is a-C, which, due to its amorphousstructure, is an insulator rather than a conductor. By thermally orelectrically annealing the deposited interface material, the a-C ispartially or totally graphitized. In other words, via thermal orelectric annealing, the deposited carbon transitions from a-C, which isinsulating, to partially or totally graphitized carbon, which isconducting. As a result, after post processing, the interface 26 is anohmic contact having low electric resistivity. Note that in theembodiment where the deposited interface material is a-C, after postprocessing, the electric resistivity of the interface 26 is low bothbecause of the conductivity of the partially or totally graphitizedcarbon interface 26 and because the partially or totally graphitizedcarbon interface 26 has a crystalline structure that is the same as, orsimilar to, that of the conduction shells of the MWCNTs 28 and 30.

FIG. 5 illustrates a system 38 for fabricating the interfaces 10 and 12between the MWCNT 14 and the interconnects 16 and 18 on the substrate 20according to one embodiment of the present disclosure. Note that thisdiscussion is equally applicable to the fabrication of the interface 26between the MWCNTs 28 and 30 as described above in FIGS. 4A through 4C.As illustrated, the substrate 20 is located within a reaction chamber40. A primary e-beam source, which in this embodiment is a ScanningElectron Microscope (SEM) 42, provides the primary e-beam for theFEB-CVD process. The system 38 may also include a precursor source 44.The precursor source 44 may operate to flood the reaction chamber 40with the precursor gas or provide the precursor gas to a localizedregion of the substrate 20 via an associated needle. Note that theprecursor source 44 is optional. In another embodiment, the precursorgas is pre-adsorbed on the surface of the substrate 20 from thecontamination or exposure to environment. Lastly, the system 38 includesa controller 46. The controller 34 is a hardware device such as, forexample, a personal computer. The controller 46 includes one or morehardware components, one or more software components, or a combinationthereof that enable the controller 46 to control the SEM 42 andoptionally the precursor source 44 and substrate 20 to fabricate theinterfaces 10 and 12 as described above. Note that the system 38 mayinclude additional components that are not illustrated in FIG. 5, aswill be appreciated by one of ordinary skill in the art upon readingthis disclosure. For example, the system 38 may include a vacuum pumpthat operates to control the pressure within the reaction chamber 40.

Those skilled in the art will recognize improvements and modificationsto the embodiments of the present invention. All such improvements andmodifications are considered within the scope of the concepts disclosedherein and the claims that follow.

1. A method comprising: aligning a multiwalled carbon nanotube (MWCNT)between two desired nodes on a substrate, the MWCNT comprising aplurality of conduction shells; and fabricating an interface between anexposed end of the MWCNT and one of the two desired nodes on thesubstrate such that the interface forms a contact with at least amajority of the plurality of conduction shells of the MWCNT at theexposed end of the MWCNT; wherein fabricating the interface comprisesperforming a Focused Electron Beam Chemical Vapor Deposition (FEB-CVD)process wherein a primary electron beam used for the FEB-CVD process isfocused near the exposed end of the MWCNT such that, during depositionof a desired interface material for the interface, surface diffusion ofprecursor molecules used for the FEB-CVD process induces spread of thedesired interface material into the exposed end of the MWCNT therebymaking connections with the at least a majority of the plurality ofconduction shells of the MWCNT.
 2. The method of claim 1 wherein theinterface forms a contact with all of the plurality of conduction shellsof the MWCNT.
 3. The method of claim 1 wherein the primary electron beamis focused at a location that is less than or equal to 500 nanometers(nm) from the exposed end of the MWCNT.
 4. The method of claim 1 whereinperforming the FEB-CVD process comprises controlling an ON/OFF timing ofthe primary electron beam during deposition of the desired interfacematerial such that surface diffusion of the precursor molecules isprovided sufficient time to induce spread of the desired interfacematerial into the exposed end of the MWCNT.
 5. The method of claim 1wherein the desired interface material is amorphous Carbon (a-C).
 6. Themethod of claim 5 further comprising performing post-processing toprovide at least partial graphitization of the a-C such that theinterface transitions from insulating to conducting.
 7. The method ofclaim 1 wherein the desired interface material is a metallic material.8. The method of claim 1 wherein fabricating the interface comprisesfabricating the interface at room temperature.
 9. The method of claim 1wherein the MWCNT initially has a closed end, and the method furthercomprises opening the closed end of the MWCNT to provide the exposed endof the MWCNT.
 10. The method of claim 1 wherein the interface is a lowelectric resistance ohmic contact between the at least a majority of theplurality of conduction shells of the MWCNT and the one of the twodesired nodes on the substrate.
 11. The method of claim 1 wherein thetwo desired nodes are two electrically conducting interconnects on thesubstrate.
 12. The method of claim 1 wherein the one of the two desirednodes is an exposed end of a second MWCNT such that the interfaceconnects at least a majority of the plurality of conduction shells ofthe MWCNT at the exposed end of the MWCNT and at least a majority of aplurality of conduction shells of the second MWCNT at the exposed end ofthe second MWCNT.
 13. A method comprising: aligning a carbon nanotube(CNT) between two desired nodes on a substrate; and performing a FocusedElectron Beam Chemical Vapor Deposition (FEB-CVD) process to deposit aninterface between an end of the CNT and one of the two desired nodes onthe substrate, wherein a primary electron beam used for the FEB-CVDprocess is focused near the end of the CNT such that, during depositionof a desired interface material for the interface, surface diffusion ofprecursor molecules used for the FEB-CVD process induces spread of thedesired interface material to make contact with the CNT.
 14. The methodof claim 13 wherein the CNT is a Multiwalled Carbon Nanotube (MWCNT) andthe interface provides a contact between at least a majority of aplurality of conduction shells of the MWCNT and the one of the twodesired nodes on the substrate.
 15. The method of claim 13 wherein theCNT is a Single Walled Carbon Nanotube (SWCNT).
 16. The method of claim13 wherein the primary electron beam is focused at a location that isless than or equal to 500 nanometers (nm) from the end of the CNT.